Actually, it works in OOS 11 too.
In OOS 11, it's slightly different than what you wrote above. For OOS 11, go to Settings < System < Languages & Input < Keyboard height adjustment < select the 'Hide' option
Follow the steps I just wrote above.
The other thing you could do is SwiftKey allows you to customize the height of the keyboard itself so you can make it taller or shorter, depending on how you like it. To do that, go your SwiftKey settings app < Layout & keys < Resize < adjust the top slider up or down to your liking (if you want to go back to the default height of the keyboard, just hit the Reset button there).
Click to expand...
